DETROIT — Sen. Bernie Sanders’s path to the Democratic nomination may be narrowing, but his record fundraising shows no sign of slowing down, ensuring that the long-shot rival to Hillary Clinton can remain in the race for months to come.

Sanders’s unique success at attracting money, combined with his appeal to young voters, means that he will keep raising and spending millions of dollars across the country – forcing Clinton to spend, too, and potentially allowing him to score enough victories to drag out the nominating contest and delay what is widely seen as Clinton’s inevitable pivot to the general election.

The lasting power of the senator from Vermont has triggered concern among Clinton allies that it will weaken her – not only because she must spend precious dollars competing against him, but also because he is criticizing her in ways that could dampen enthusiasm for her in the fall. But other supporters note that Sanders’s success has helped keep the Clinton campaign at a full tilt.

“We planned for a competitive primary and have beaten every goal we set for ourselves,” said Clinton campaign spokesman Josh Schwerin. “Thanks to smart investments, we have a commanding delegate lead and, as of the last filing, a 2-to-1 cash-on-hand advantage.”

But Sanders’s ability to raise millions from small-dollar donors has allowed him to press his case that she is overly reliant on wealthy donors.